1. Field of the Invention
The present invention relates to a device which detects a particulate matter included in an exhaust gas from a diesel engine or the like.
2. Description of the Related Art
An exhaust gas from a diesel engine or the like includes a particulate matter ((PM) detected as three components of an organic solvent soluble component, soot and sulfate), and this particulate matter has been a cause for air pollution. In particular, when a defect occurs in a particulate matter generation source such as the diesel engine, the particulate matter in the exhaust gas discharged to atmospheric air increases, and noticeably adversely affects the environment. To prevent this problem, it is essential to detect the particulate matter in the exhaust gas and to recognize the defect in the diesel engine or the like.
Moreover, in recent years, to prevent the pollution and improve the environment, a diesel particulate filter (DPF) has been incorporated in an exhaust system or the like and used for the treatment of the exhaust gas. This DPF is usually made of a ceramic material, has a high reliability and hence can be used for a long period of time. However, it cannot be considered that there is not any possibility of the occurrence of a defect such as cracking due to heat deterioration or the like. If there is such a possibility, the particulate matter leaks though its amount is small. To prevent this problem, it is important to detect the particulate matter in the exhaust gas treated by the DPF and to immediately detect the occurrence of the defect.
It is to be noted that examples of a prior document include Patent Document 1. In Patent Document 1, a particulate matter detection device is disclosed in which the particulate matter is charged by corona discharge to measure the ion current thereof, thereby measuring the amount of the particulate matter.
[Patent Document 1] JP-A-60-123761
However, in the method described in Patent Document 1, the ion current for charging the particulate matter is weak, whereby a large-scale detection circuit for detecting the weak ion current is required, and the device becomes expensive. Additionally, when the flow rate of the exhaust gas is large, the particulate matter cannot effectively be charged, and a measured value is smaller than the amount of the particulate matter actually contained in the exhaust gas, whereby there is room for the improvement of precision. There has also been a problem that electrodes and the like are corroded by acid or alkali in the exhaust gas.
The present invention has been developed in view of such a situation, and an object thereof is to provide a particulate matter detection device which can easily and inexpensively detect the particulate matter, which has a high measurement precision and which is excellent in corrosion resistance of measurement electrodes.